Drop-out fire vents are used in the roofs of commercial buildings and are designed to open automatically to release smoke and heat in the event of fire within the building. A typical drop-out fire vent has an appearance similar to a skylight and comprises a frame or "curb" that is installed over a vent opening in the roof of the building. A plastic cover or dome is carried by the frame and is made of a plastic material that will soften when exposed to heat, e.g. PVC, acrylic or polycarbonate. Around its perimeter, the cover is coupled to the curb by a retainer frame that is designed to provide weather-tightness, while allowing the dome to pull away and fall into the building as the dome loses structural integrity with increasing temperature.
The domes themselves typically are translucent mouldings so that the vent normally serves as a skylight allowing natural daylight into the building. The dome may be a so-called "QUADRI-DOME" for example as disclosed in U.S. Pat. No. 3,918,226. An existing curb frame design is disclosed in U.S. Pat. No. 4,080,763.
A disadvantage of existing drop-out fire vents is that the precise temperature at which the dome will drop out can vary and typically is quite low compared with the temperature at which a water sprinkler system within the building might be triggered. For example, a fire vent dome may lose structural integrity at a temperature in the region of 160.degree. F. if it is made of PVC, or a temperature as high as 250.degree. F. if it is made of a polycarbonate material. On the other hand, sprinkler systems may require a trigger temperature over 300.degree. F. If the dome drops out before the sprinkler system is triggered, there can be a cooling effect as hot air is vented from the building sufficient to prevent the sprinklers reaching their trigger temperature. In fact, in some jurisdictions, building codes prohibit the use of drop-out fire vents in buildings that are equipped with sprinkler systems, particularly so-called "early suppression--fast response" (ESFR) systems that are designed to dump large volumes of water into the building in a short period of time.
On the other hand, practical experience has been that sprinkler systems sometimes fail to operate correctly. For example, a sprinkler system may be in place in the building for many years before a situation arises in which the sprinkler is required to perform. Over the years, the sprinkler system can deteriorate or sometimes even be shut off for maintenance and never turned back on again, with the result that the sprinkler will not operate when there is a fire. Bearing this in mind, fire departments generally favour installation of vents so that smoke will be removed in the event of a fire, improving visibility for firemen who may have to enter the building. If there are no vents, firemen sometimes will even break holes in the roof of a building to let smoke out.
Another factor of course is that different types of fires emit different amounts of smoke and heat. As such, any fire suppression system should offer a "balanced" approach.
Spring-activated "pop-up" vents are available, although they have their own disadvantages. This type of vent can be designed to open at a fairly precise elevated temperature, but is relatively complex and expensive to manufacture. Also, the vent must be capable of moving to its full open position against the effects of the wind, snow, ice and debris that may have accumulated on the vent over the years. Mechanical spring-driven struts that are used to open the vent are prone to deteriorate with time. Reliability of operation is a concern.
Accordingly, an object of the present invention is to provide a fire vent that address the factors outlined above and that can be used effectively in combination with EFSR and other sprinkler systems.